Electromagnetic scattering by inhomogeneous dielectric cylinders

The scattering of electromagnetic waves by inhomogeneous dielectric cylinders is formulated by the unimoment method, and the interior finite-element problem is solved in a mesh geometry that greatly increases computational efficiency. Results are presented and compared to previously reported curves.     

Electromagnetic scattering from longitudinally corrugated cylinders

The scattering of plane electromagnetic waves from circular cross-section cylinders, longitudinally corrugated to realize anisotropic structures, is analyzed. The solution is devised at oblique incidence and for an arbitrary polarization of the incident wave using a rigorous Floquet modal expansion of the field. The implementation of the procedure is discussed with emphasis to its numerical efficiency     

Electromagnetic scattering from two adjacent cylinders

The problem of electromagnetic scattering from two adjacent cylinders is considered. The approximate analytical scattering solutions up to second order are derived for two adjacent, long finite length cylinders. The method used can avoid the complex evaluation of scattering field under nonplane wave illustrated when calculating the secondary scattering fields. The bistatic specular scattering is discussed, and the results are compared with numerical computations based on the method of moments     

Electromagnetic scattering by rough conducting circular cylinders.II. Axial corrugation

For pt.I see ibid., vol.36, no.5, p.651 (1988). The coherent and incoherent responses of conducting axially corrugated surfaces (which are on the average circular cylinders) are calculated. The calculation encompasses second-order perturbation. The general approach used is to apply the extinction theorem to write an integral equation for the surface current density, and then to use the perturbation theory to solve it. The results are recast by using Pade approximants to achieve a significant extension of the domain of validity of the original formulation     

Electromagnetic scattering from anisotropic plasma-coated perfect electromagnetic conductor cylinders

The scattering of electromagnetic waves by a perfect electromagnetic conductor (PEMC) cylinder coated with a homogeneous plasma anisotropic material is studied in this paper. Both of the transverse electric and the transverse magnetic polarizations of the incident waves have been analyzed and formulated. The presented analysis and formulations are general for any perfect conductor cylinder (PEC, PMC, or PEMC) with general isotropic/anisotropic material coatings that include plasma and metamaterials. The co-polarized and the cross-polarized components of the scattered fields are computed for different cases of the anisotropic plasma coated PEMC cylinders and for an anisotropic plasma column. Bistatic echo widths for the cases of PEMC, PEC (perfect electric conductor) and PMC (perfect magnetic conductor) cores have been computed and compared. The behavior of the monostatic echo width with the variation of the admittance parameter for the co-polarized and the cross polarized fields is also investigated. The comparisons of the computed results of the presented formulations with the published results of some special cases confirm the accuracy of the presented analysis.     

Electromagnetic scattering by rough conduction circular cylinders.I. Angular corrugation

The coherent and incoherent responses of perfectly conducting, angularly corrugated surfaces (which are infinite circular cylinders on the average) are calculated using a second-order perturbation method. The general approach used is to apply the extinction theorem to write an integral equation for the surface current density, and then to use perturbation theory to solve it. These results are recast by using the only nontrivial Pade approximant for this approximation. This recasting yield a considerable qualitative improvement which, at least in one special case, is shown to be quantitative as well     

Transient scattering by resistive cylinders

The two-dimensional scattering of an electromagnetic pulse normally incident on a collection of infinitely long cylinders of arbitrary shape is considered. ForE-polarization an electric field integral equation is derived that is applicable to solid cylinders and/or thin sheets, resistive and/or perfectly conducting. The contribution of the self-cell at later times is carefully analyzed. The expression obtained represents a generalization of previously known results. For an incident Gaussian pulse, numerical results are presented for surface currents and far-fields, for perfectly conducting and resistive circular cylinders and strips. A fast Fourier transform (FFT) algorithm is implemented to obtain the backscattering radar cross section, which is in good agreement with results obtained from either exact continuous wave (CW) solutions or the method of moments.     

Low-frequency scattering by rectangular cylinders

An integral equation formulation is used to investigate potential problems associated with low-frequency scattering by both dielectric and perfectly conducting cylinders of rectangular cross section. Induced dipoles and scattering cross sections are obtained for 1) waves withbar{E}orbar{H}parallel to the axis, and 2) directions of propagation perpendicular and parallel to the broad side of the rectangle.     

Electromagnetic scattering from nonlinear anisotropic cylinders. I.Fundamental frequency

The solution of the problem of electromagnetic scattering of obliquely incident plane waves by homogeneous, nonlinear anisotropic cylindrical structures is obtained. The medium of the scatterer is characterized by Volterra-type integrals for the electric and magnetic flux density vectors D and B, respectively. The nonlinear problem is solved using the perturbation method. The effects of nonlinearities on the field properties both inside and outside the scatterer, together with the effect on the radar cross section, are investigated for the fundamental frequency components. To demonstrate the validity of the approach, the results obtained by the perturbation method are compared with those obtained using the plane wave representation method of D. Censor (1983), where the iteration method is used to solve the resulting dispersion equation. The results are in very good agreement in both amplitude and phase of the fields for the case of very weak nonlinearity. When the relative magnitude of the nonlinear component of the permittivity is increased, the iteration method shows a faster divergence of the phase from the linear phase     

Antenna pattern scattering by rectangular cylinders

The uniform geometrical theory of diffraction (UTD) and the complex source point method are combined to predict two-dimensional (2-D) scattering by rectangular cylinders for E and H-polarized beam sources. Arrays of such beam solutions are also used to model propagation of radio beams into the shadow regions of buildings for local extended sources. Direct numerical verification of the results is obtained for square cylinders of moderate width     

Multiple scattering by two conducting circular cylinders

Multiple scattering by two conducting circular cylinders is studied by applying three different methods: the method of Zitron and Karp (ZK), the method of Karp and Russek, and an iterative method which gives the exact solution. It is found from the numerical results for the total scattering cross section that the ZK method gives very precise results even for rather largekaand smallkd, whereaanddare the radius of the cylinder and the separation between the cylinders, respectively.     

Electromagnetic scattering from conducting circular cylinders inthe presence of a stratified anisotropic medium-TM case

Scattering by a conducting circular cylinder in the presence of a stratified ferrite medium is investigated analytically using a combined Green's function (G-function) and integral equation approach. The incident plane wave is polarized along the axis of the cylinder. The bias DC magnetic field is in the same direction. The G-function of the structure is developed by well-known techniques of matrix analysis, and the appropriate integral equation for the electric field is derived on the basis of the modified reciprocity theorem. Its solution is followed by numerical results presented in graphical form for both the current density induced on the scatterer's surface and the scattered far field. The possibility of controlling the scattering properties of the structure by varying the degree of anisotropy is also investigated. The main conclusion is that anisotropic materials can be used to control antenna radiation characteristics     

Electromagnetic scattering by indented screens

The problem of three dimensional electromagnetic scattering from a perfectly conducting screen with a bounded indentation is formulated as a system of boundary integral equations for the electric current density on the cavity wall and the interface between the cavity and free space. It is shown how the fictitious current density on the interface may be eliminated resulting in an integral equation of the second kind for the current density on the cavity wall only, with no integration over the infinite screen. In addition, integral representations are derived that represent the field everywhere in space in terms of the current density on the cavity wall only. Furthermore, asymptotic expressions for the far field are also presented. The equations and representations simplify considerably in the two-dimensional scalar case and results are presented for both TE and TM polarization     

Electromagnetic scattering from a 2-D chiral strip simulated by circular cylinders for uniform and nonuniform chirality distribution

A semi-analytical solution is presented to the problem of electromagnetic scattering from an incident plane wave on a rectangular strip. The strip is simulated by parallel circular cylinders, illuminated by either a TE/sub z/ or a TM/sub z/ incident plane wave. The solution is based on the application of the boundary conditions on the surface of each cylinder in terms of the local coordinate system of each individual cylinder. This technique is used to predict the radar cross-section of strips composed of dielectric, conducting, and chiral material with uniform or nonuniform chiral admittance distribution.     

Electromagnetic inverse scattering of multiple perfectly conducting cylinders by differential evolution strategy with individuals in groups (GDES)

The differential evolution strategy with individuals in groups (GDES) is proposed to solve the electromagnetic inverse scattering of multiple perfectly conducting cylinders with transverse magnetic wave incidence. The inverse problem is to locate the cylinders and reconstruct their contours, besides the determination on the number of cylinders. The governing electric field integral equations for the scattering problem are expressed as surface integrals over the cylinder contours. The scattering problem is solved using point-matching method with pulse basis and Dirac test functions. The inverse problem is cast into an optimization problem and solved using the GDES. Numerical reconstruction results show that both the quality of the reconstructed profile and the convergence performance are significantly improved, as compared to the original DES.     

Inverse scattering of dielectric cylinders by a cascaded TE-TMmethod

A novel approach for inverse scattering of dielectric objects Is proposed. This reconstruction algorithm aims to synthesize individual TE and TM inverse scattering in order to decrease the effect of ill-posedness. The proposed synthesizing method has a cascade structure composed of TE and TM inverse scattering algorithms. Appropriate approaches are adopted in these two algorithms to take advantage of the physical difference between them. A diversity scheme of multiple incident views and receiving points is also incorporated. Numerical simulations are conducted to compare the proposed synthesizing method with two other methods using individual TE or TM information. Some advantages of the synthesizing method are also observed     

Electromagnetic scattering by a helical sheath

The harmonic-series solution for the scattering by a unidirectionally conducting helical sheath is obtained when the medium external to the sheath is different from the internal one. The expressions for the scattering cross-sections and surface charge density are also given.